Pre-formed thermoplastic filler for thermoset structure

ABSTRACT

An apparatus includes a first thermoset layer that includes a first fibrous material embedded in a first thermoset matrix. The apparatus also includes a second thermoset layer that includes a second fibrous material embedded in a second thermoset matrix. The second thermoset layer is coupled to the first thermoset layer to form a joint. Further, a gap is defined between the first thermoset layer and the second thermoset layer. The apparatus also includes a thermoplastic filler that is made from a thermoplastic material. The thermoplastic filler is positioned within the gap.

FIELD

This disclosure relates generally to complex structures made fromthermoset materials, and more particularly to the formation of jointsadjoining layers of thermoset materials.

BACKGROUND

Today, many complex structures, such as aircraft, spacecraft,automobiles, and the like, are made from composite materials. Compositematerials typically include fibrous materials embedded in a matrix madefrom thermoset materials. Uncured thermoset materials are arranged in adesired manner and then cured to harden the matrix. Like complexstructures made from more traditional materials, such as metal, complexstructures made from composite materials include a significantly largenumber of interconnected components. The interconnected components ofcomplex structures are connected together at joints. The joints ofconventional complex structures are traditionally formed using fastenersand weldments. However, the joints of some complex structures formedfrom composite materials are formed using adhesives and co-curing ofthermoset materials.

To improve the characteristics of joints between components made fromcomposite materials, the components incorporate bends at the joints,which introduce gaps within the joints. Often, the gaps are filled withthermoset materials that cure concurrently with the thermoset materialsforming the components. Because uncured thermoset materials are flexibleand pliable, before and during curing, maintaining such materials inplace can be difficult. Additionally, after curing, thermoset jointfillers are susceptible to cracking due to thermal and mechanical staticand fatigue loads.

SUMMARY

The subject matter of the present application has been developed inresponse to the present state of the art, and in particular, in responseto the problem of, and the need to mitigate, crack formation incomponents of various systems, such as aircraft, that have not yet beenfully solved by currently available techniques. Accordingly, the subjectmatter of the present application has been developed to provide anapparatus, system, and method for mitigating the formation of cracks inmulti-component systems, such as an aircraft, that overcome at leastsome of the above-discussed shortcomings of prior art techniques.

According to one embodiment, an apparatus includes a first thermosetlayer that includes a first fibrous material embedded in a firstthermoset matrix. The apparatus also includes a second thermoset layerthat includes a second fibrous material embedded in a second thermosetmatrix. The second thermoset layer is coupled to the first thermosetlayer to form a joint. Further, a gap is defined between the firstthermoset layer and the second thermoset layer. The apparatus alsoincludes a thermoplastic filler that is made from a thermoplasticmaterial. The thermoplastic filler is positioned within the gap.

In some implementations, the apparatus also includes a third thermosetlayer that includes a third fibrous material embedded in a thirdthermoset matrix. The third thermoset layer is coupled to the first andsecond thermoset layers to form the joint. The gap is defined betweenthe first, second, and third thermoset layers. The gap can have agenerally triangular-shaped cross-section and the thermoplastic fillercan have a generally triangular-shaped cross-section corresponding withthe generally triangular-shaped cross-section of the gap. Across-sectional shape of the gap and the thermoplastic filler can besubstantially non-symmetrical.

According to some implementations, the first and second fibrous materialincludes carbon fibers. The first and second thermoset matrices may eachinclude a cured cross-linked material. The thermoplastic material may bea non-curable and non-cross-linkable material. Further, a curetemperature of each of the first and second matrices can be less than amelting point of the thermoplastic material.

In certain implementations, the first thermoset layer includes a firstbent portion that has a first radius of curvature. The first bentportion defines the gap. The thermoplastic filler includes a firstcurved surface that has a second radius of curvature that correspondswith the first radius of curvature. The second thermoset layer caninclude a second bent portion that has a third radius of curvature. Thesecond bent portion can define the gap, and the thermoplastic filler caninclude a second curved surface that has a fourth radius of curvaturethat corresponds with the third radius of curvature. The first, second,third, and fourth radii of curvature can be the same. The first andsecond radii of curvature can be the same, and the third and fourthradii of curvature can be the same, where the first and second radii ofcurvature are different than the third and fourth radii of curvature.The apparatus may also include a third thermoset layer that includes athird fibrous material embedded in a third thermoset matrix. The thirdthermoset layer can include a planar portion that defines the gap, andthe thermoplastic filler can include a flat surface that correspondswith the planar portion of the third thermoset layer.

According to yet another embodiment, a method for making a joint for astructure includes forming a thermoplastic filler made from athermoplastic material. The method also includes applying an uncuredfirst thermoset layer onto the thermoplastic filler, where the uncuredfirst thermoset layer includes a first fibrous material embedded in afirst thermoset matrix. Additionally, the method includes applying anuncured second thermoset layer onto the thermoplastic filler and intocontact with the uncured first thermoset layer, where the uncured secondthermoset layer includes a second fibrous material embedded in a secondthermoset matrix. While the uncured first and second thermoset layersare applied onto the thermoplastic filler and while the uncured secondthermoset layer contacts the uncured first thermoset layer, the methodincludes curing the uncured first and second thermoset layers andbonding together the first thermoset layer, second thermoset layer, andthermoplastic filler.

In some implementations of the method, the uncured first and secondthermoset layers are cured at a temperature below a melting temperatureof the thermoplastic material. The method can further include applyingan uncured third thermoset layer onto the thermoplastic filler, wherethe uncured third thermoset layer includes a third fibrous materialembedded in a third thermoset matrix. Forming the thermoplastic fillercan include compression molding the thermoplastic material.Alternatively, forming the thermoplastic filler can include extrudingthe thermoplastic material.

In certain implementations of the method, forming the thermoplasticfiller includes forming at least one concave surface in thethermoplastic filler. Applying the uncured first thermoset layer ontothe thermoplastic filler can include bending the uncured first thermosetlayer along the at least one concave surface, and curing the uncuredfirst thermoset layer can include curing the uncured first thermosetlayer while bent along the at least one concave surface.

According to another embodiment, an aircraft includes a first layer madefrom a thermoset carbon-fiber composite material and a second layer madefrom a thermoset carbon-fiber composite material. The second layer iscoupled to the first layer to form a joint and to define a gap betweenthe first and second layers. The aircraft also includes a hardenedfiller made from a thermoplastic material positioned within the gap.

The described features, structures, advantages, and/or characteristicsof the subject matter of the present disclosure may be combined in anysuitable manner in one or more embodiments and/or implementations. Inthe following description, numerous specific details are provided toimpart a thorough understanding of embodiments of the subject matter ofthe present disclosure. One skilled in the relevant art will recognizethat the subject matter of the present disclosure may be practicedwithout one or more of the specific features, details, components,materials, and/or methods of a particular embodiment or implementation.In other instances, additional features and advantages may be recognizedin certain embodiments and/or implementations that may not be present inall embodiments or implementations. Further, in some instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the subject matter ofthe present disclosure. The features and advantages of the subjectmatter of the present disclosure will become more fully apparent fromthe following description and appended claims, or may be learned by thepractice of the subject matter as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the subject matter may be more readilyunderstood, a more particular description of the subject matter brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the subject matter and arenot therefore to be considered to be limiting of its scope, the subjectmatter will be described and explained with additional specificity anddetail through the use of the drawings, in which:

FIG. 1 is a top plan view of an aircraft showing a detailedcross-sectional view of a joint of the aircraft according to oneembodiment;

FIG. 2 is a cross-sectional perspective view of a joint of an aircraftaccording to one embodiment;

FIG. 3 is a cross-sectional side view of a joint of complex structuremade from composite materials according to one embodiment;

FIG. 4 is a cross-sectional side view of a joint of complex structuremade from composite materials according to another embodiment;

FIG. 5 is a cross-sectional side view of a joint of complex structuremade from composite materials according to yet another embodiment; and

FIG. 6 is a schematic flow diagram of a method for making a joint in acomplex structure made from composite materials according to oneembodiment.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment. Similarly, the use of theterm “implementation” means an implementation having a particularfeature, structure, or characteristic described in connection with oneor more embodiments of the present disclosure, however, absent anexpress correlation to indicate otherwise, an implementation may beassociated with one or more embodiments.

Referring to FIG. 1, one embodiment of an aircraft 10 is shown. Theaircraft 10 can be any of various aircraft, such as commercial aircraftused for the transportation of passengers, military aircraft formilitary operations, personal aircraft, and the like. Moreover, althoughan aircraft is depicted in the illustrated embodiments, in otherembodiments, another complex structure, such as a vehicle (e.g.,helicopter, boat, spacecraft, automobile, etc.) or non-mobile complexstructure (e.g., building, bridge, machinery, etc.) can be used. Asdefined herein, a complex structure includes any multi-componentstructures in a fully operative state to fulfill the intended purpose ofthe structure.

The depicted aircraft 10 includes a body 12 (e.g., fuselage), a pair ofwings 14 coupled to and extending from the body 12, a verticalstabilizer 16 coupled to the body, and a pair of horizontal stabilizers18 coupled to the body and/or the vertical stabilizer. The aircraft 10can be any of various types of aircraft, such as a passenger airplane, afighter jet, a helicopter, spacecraft, and the like. As depicted, theaircraft 10 represents a passenger airplane.

Generally, the body 12, wings 14, vertical stabilizer 16, and horizontalstabilizers 18 of the aircraft each includes an internal frame envelopedby a cover or skin. The cover is coupled to the frame to form anexterior shell of the aircraft. Most commonly, the cover is coupled tothe frame using a plurality of fasteners that extend through the coverand engage the frame. For sealing, insulation, electrical conduction,and/or aesthetic effects, one or more additional components can becoupled to an exterior of the cover. For example, one or more coatingscan be applied onto the cover. The coatings can include one or more of asealant coating made from any of various materials, such as aninsulation material, dielectric material, a paint coating, a conductivematerial coating, or a coating embedded with structural components, suchas a conductive mesh or layer.

One or both of the cover and internal frame can be made from one or morelayers of a composite fiber material or fiber-reinforced polymer. Thecomposite fiber material includes a curable thermoset matrix, such as apolymer-based matrix, with reinforced fibers, such as carbon-basedfibers, glass-based fibers, and the like. The layers of composite fibermaterial may be coupled together to form a joint. Generally, a joint inthe cover or frame of the aircraft 10 is formed by adjoining at leasttwo layers of uncured composite fiber material, and co-curing the twolayers by applying heat to the layers. The heat applied to the layershas a temperature above a curing temperature of the thermoset matrix toharden the matrix. Curing the thermoset matrix of the composite fibermaterial induces irreversible chemical reactions that create permanentconnections (e.g., cross-links) between the molecular chains of thematrix. The formation of permanent cross-links adds a three-dimensionalstructure to the composite fiber material, as well as increases therigidity of the material. After curing, the thermoset matrix of thecomposite fiber cannot return to the uncured state by re-melting thematrix in the same manner as a thermoplastic material. In other words,curing the thermoset matrix permanently changes the chemical structureof the thermoset matrix.

According to one embodiment, as shown in the detailed view of FIG. 1,the cover and/or internal frame of the aircraft 10 can include a joint20 formed at the intercoupling of multiple thermoset layers 22, 24A, 24B(e.g., sheets). Each thermoset layer 22, 24A, 24B is made fromreinforced fibers or fibrous material embedded in a thermoset matrix. Incertain implementations, while the thermoset layers 22, 24A, 24B are inan uncured “pre-impregnated” state, they are arranged in contact witheach other and against a thermoplastic filler 26 to form the joint 20.With the uncured thermoset layers 22, 24A, 24B arranged to form thejoint 20 about the thermoplastic filler 26, the thermoset layers arecured in place by the application of heat at or above a cure temperatureassociated with the thermoset matrix. Curing the thermoset layers 22,24A, 24B while in contact with each other results in the thermosetmatrices of adjacent layers bonding with each other to fixedly couplethe layers together.

The thermoset layers 22, 24A, 24B of the joint 20 may have any ofvarious thicknesses, compositions, and configurations. For example, eachthermoset layer 22, 24A, 24B can include multiple sub-layers ofcomposite fiber material with the fibers of each layer being oriented inthe same or a different manner. Further, the thermoset layers 22, 24A,24B may form any of various structural features of the aircraft 10. Forexample, in one implementation, the thermoset layer 22 may act as anouter layer (e.g., cover) of the aircraft 10, and the thermoset layers24A, 24B may act as inner layers (e.g., frame) of the aircraft. In otherimplementations, all the thermoset layers 22, 24A, 24B act as outerlayers of the aircraft, or all of the thermoset layers act as innerlayers of the aircraft.

In the illustrated embodiment, the thermoset layer 22 includes asubstantially flat portion 23 proximate the joint 20. In contrast, thethermoset layers 24A, 24B each includes a bent portion 38A, 38B,respectively, and respective flat portions 39A, 39B, 41A, 41B extendingfrom the respective bent portions proximate the joint 20. Morespecifically, the joint 20 is formed by fixedly coupling together theinner surfaces 36A, 36B of corresponding planer portions 41A, 41B of thethermoset layers 24A, 24B, fixedly coupling together the inner surface36A of the flat portion 39A of the thermoset layer 24A and an innersurface 32 of a section of the flat portion 23 of the thermoset layer22, and fixedly coupling together the inner surface 36B of the flatportion 39B of the thermoset layer 24B and the inner surface 32 ofanother section of the flat portion 23 of the thermoset layer 22. Theinner surfaces 32, 36A, 36B of the thermoset layers 22, 24A, 24B opposecorresponding outer surfaces 30, 34A, 34B of the thermoset layers.

When the joint 20 is formed, a gap 28 or space is defined between theinner surfaces 36A, 36B of the bent portions 38A, 38B of the thermosetlayers 24A, 24B, and the inner surface 32 of the flat portion 23 of thethermoset layer 22. Accordingly, the gap 28 has a cross-sectional shapedefined by the inner surfaces 32, 36A, 36B of the thermoset layers 22,24A, 24B. In the illustrated embodiment of FIG. 1, the gap 28 has agenerally triangular cross-sectional shape. The inner surfaces 36A, 36Bof the bent portions 38A, 38B are curved to have any of various radii ofcurvature. Accordingly, the two curved sides of the gap 28 may have anyof various radii of curvature corresponding with the radii of curvatureof the inner surfaces 36A, 36B of the bent portions 38A, 38B. In someimplementations, such as shown in FIG. 1, the bent portions 38A, 38B canbe bent to the same degree such that the radii of curvature of the innersurfaces 36A, 36B, and the two curved sides of the gap 28, are the same.In contrast, in other implementations, such as shown in the joint 120 ofFIG. 3, the bent portions 138A, 138B can be bent at different degreessuch that the radii of curvature of the curved surfaces 140A, 140B, andthe two curved sides of the gap 128, are different. For example, thebent portion 138B of the thermoset layer 124B is bent at a sharper anglethan the bent portion 138A of the thermoset layer 124A such that theradius of curvature of the curved surface 140B of the bent portion 138B,and associated curved side of the gap 128, is less than the radius ofcurvature of the curved surface 140A of the bent portion 138A, and theassociated curved side of the gap.

The thermoplastic filler 26 of the joint 20 is located or positionedwithin the gap 128. In certain implementations, the thermoplastic filler26 is closely fitted within the gap 128 and provides support to thethermoset layers 22, 24A, 24B, which increases the overall strength ofthe joint 20 and improves the stiffness of the joint. Further, thethermoplastic filler 26 mitigates the formation of micro-cracks andmacro-cracks in the thermoset layers 22, 24A, 24B.

The thermoplastic filler 26 is made from a thermoplastic material. Incontrast to the thermoset material of the thermoset layers,thermoplastic material of the filler 26 softens upon the application ofheat, and hardens upon the removal of heat. Additionally, different thanthermoset materials, the transformation of thermoplastic materialsbetween a hardened state and a pliable state involves only a physicaltransformation, as opposed to the chemical transformation (e.g.,cross-linking) of a cured thermoset material. Therefore, thetransformation of the thermoplastic materials between hardened andpliable states is reversible. In some implementations, the thermoplasticmaterial of the filler 26 is embedded with fibrous materials.

Generally, a thermoplastic material in a hardened state becomes pliable(e.g., unstable) at a melting temperature of the thermoplastic material.In some embodiments, the melting temperature of the thermoplasticmaterial of the filler 26 is higher than the curing temperature of thethermoset material of the thermoset layers 22, 24A, 24B. According tosome implementations, the melting temperature of the thermoplasticmaterial of the filler 26 is greater than between about 450° F. and 750°F., and the curing temperature of the thermoset material of thethermoset layers 22, 24A, 24B is between about 300° F. and about 400° F.In one implementation, the melting temperature of the thermoplasticmaterial is about 710° F. and the curing temperature of the thermosetmaterial is about 355° F. According to some implementations, a ratio ofthe melting temperature of the thermoplastic material to the curingtemperature of the thermoset material is between about 1.125 and about2.5. In one specific implementation, the ratio of the meltingtemperature of the thermoplastic material to the curing temperature ofthe thermoset material is about 2.

Referring to FIGS. 1 and 2, the thermoplastic filler 26 has across-sectional shape and size corresponding with the cross-sectionalshape and size of the gap 28. Accordingly, in the illustrated embodimentof FIG. 1, the thermoplastic filler 26 has a generally triangularcross-sectional shape with one flat side 42 and two curved sides 40A,40B (with corresponding curved surfaces). The flat side 42 correspondswith the inner surface 32 of the flat portion 23 of the thermoset layer22. The surfaces of the two curved sides 40A, 40B each have a radius ofcurvature that corresponds with the radius of curvature of therespective inner surfaces 36A, 36B of the thermoset layers 24A, 24B. Incertain embodiments, the radii of curvature of the two curved sides 40A,40B of the filler 26 are substantially the same as, or just smallerthan, the radii of curvature of the respective inner surfaces 36A, 36Bof the thermoset layers 24A, 24B. In this manner, the thermoplasticfiller 26 is configured to nestably engage the inner surfaces 32, 36A,36B of the thermoset layers 22, 24A, 24B. In some implementations, thethermoplastic filler 26 is configured to create an interference fitbetween the inner surfaces 32, 36A, 36B of the thermoset layers 22, 24A,24B and the sides 42, 40A, 40B of the filler.

As shown in FIG. 2, the joint 20 and thermoplastic filler 26 extendlengthwise along the thermoset layers 22, 24A, 24B. Accordingly, thejoint 20 and thermoplastic filler 26 each has a length that extendstransversely relative to the cross-section of the joint 20 and filler asshown in FIG. 1. In some embodiments, the length of the filler 26 isapproximately equal to the length of the joint 20. However, in otherembodiments, the filler 26 may have a length that is less or more thanthe length of the joint 20. In FIG. 2, a length of the thermoset layers22, 24A, 24B is truncated to show the cross-sectional shapes of thethermoset layers, as well as to show a perspective view of thethermoplastic filler 26.

The thermoplastic filler 26 is pre-formed before assembly of the joint20 based on the desired size and shape of the gap 28. In other words,prior to the thermoset layers 22, 24A, 24B being brought together andcured about the thermoplastic filler 26, a desired size and shape of ajoint gap is determined, and the filler is made according to the desiredsize and shape of the joint gap. Accordingly, the filler 26 is made in amanufacturing process separate from the assembly and curing processes ofthe thermoset layers 22, 24A, 24B. The thermoplastic filler 26 can bemade by using any of various manufacturing processes known in the art tobe conducive to the manufacture of thermoplastic materials. For example,in one embodiment, the thermoplastic filler 26 can be made using acontinuous compression molding technique, which includes compressing athermoplastic material (often in pellet or varying directional layers ofunidirectional composite material (e.g., pre-impregnated compositefibers)) into a heated compression mold channel with a cross-sectionsized and shaped according to the desired cross-sectional size and shapeof the filler. In other embodiments, the thermoplastic filler 26 is madeusing a continuous extrusion technique, which includes pushing orpulling melted thermoplastic material through a heated die that shapesthe material into the desired filler size and shape. According to someembodiments, the thermoplastic filler 26 can be made using machiningtechniques by machining a hardened piece of thermoplastic material. Forexample, the joint 20 may be configured to define a gap 28 with anon-uniform cross-sectional size and/or shape along a length of thejoint. Machining techniques can be used to make a thermoplastic filler26 that matches the non-uniform cross-sectional size and/or shape of thegap 28 that may be less practical to achieve using continuouscompressing molding or extrusion techniques.

A pre-formed thermoplastic filler 26 can be used as a guide to properlyposition, support, and orient the uncured thermoset layers forming thejoint 20. Uncured pre-impregnated thermoset layers or sheets are pliableand flexible, while the pre-formed thermoplastic filler 26 is hard andstiff. Accordingly, the uncured thermoset layers 22, 24A, 24B formingthe joint can be applied onto or about the thermoplastic filler 26,which can support and maintain the shape of the uncured thermoset layersprior to and during the curing process of the layers.

According to some embodiments, the cross-sectional shape of the gapdefined by the joint, and the cross-sectional shape of the thermoplasticfiller, can be non-symmetrical. For example, as shown in FIG. 3, thesmaller radius of curvature of the bent portion 138B of the thermosetlayer 124B results in the curved surface 140B of the thermoplasticfiller 126 having a smaller radius of curvature than the curved surface140A. Because the radii of curvature of the curved surfaces 140A, 140Bof the thermoplastic filler 126 are different, the cross-sectional shapeof the filler 126 is non-symmetrical. Additionally, in some embodiments,the flat portion 23 can be replaced with a bent portion similar to bentportions 38A, 38B. Accordingly, the surface 42 (e.g., flat side) of thethermoplastic filler 26 can be curved in a manner similar to curvedsides 40A, 40B of the filler to match the curvature of the bent portionreplacing the flat portion 23 in such embodiments.

Further, although the joints shown in the embodiments of FIGS. 1-3 areformed from three thermoset layers, in other embodiments, the joint canbe formed from two or more than three thermoset layers. For example, asshown in a hat stiffener or stringer configuration of FIG. 4, each oftwo joints 220 is formed from two thermoset layers 222, 224. Each joint220 includes a respective thermoplastic filler 226A, 226B located withina space between the thermoset layers 222, 224. Each thermoplastic filler226A, 226B includes surfaces that engage the thermoset layers 222, 224,and a respective surface 240A, 240B that engages a core thermoset layer228 positioned between the thermoset layers 222, 224. In someimplementations, the core thermoset layer positioned between thethermoset layers can be solid as shown in FIG. 4, or in otherimplementations, the core thermoset layer can be a relatively thin layeror layers of thermoset material with a hollow core (e.g., a plurality ofinner-wrapped plied). In yet certain implementations, no core thermosetlayer 228 is used and the surfaces 240A, 240B do not engage (e.g.,support) thermoset layers. Additionally, like the thermoset layer 224 ofFIG. 4, a single thermoset layer can form multiple joints. For example,as shown in an I-stiffener configuration of FIG. 5, each of the two bentportions of the dual thermoset layers 324A, 324B at least partiallydefines one of two gaps in which a respective thermoplastic filler 342A,342B is located. The gaps are further defined by two flat portions ofrespective thermoset layers 322A, 322B.

Although the joints shown in the embodiments of FIGS. 1-3 include athermoplastic filler with a generally triangular cross-sectional shape,in other embodiments, the thermoplastic filler can have across-sectional shape other than triangular. For example, some jointsmay be formed by more than three thermoset layers such that the jointgap and associated thermoplastic filler has polygonal cross-sectionalshape with four or more sides.

Referring to FIG. 6, and according to one embodiment, a method 400 formaking a joint in a structure includes determining the size and shape ofa gap defined by a joint made from a thermoset material at 410. The step410 is performed before the joint in formed, and can be performed duringthe design phase of the structure. In some implementations, based on thedesired design of a structure, and more specifically, the desiredconfiguration of adjoining thermoset layers of a joint, the resultantsize and shape of the gap defined between the layers can be predicted orestimated. The prediction or estimation of the size and shape of the gapmay take into account a predicted shrinkage of the thermoset materialduring curing. In some implementations, the thermoset material isdesigned to be bent or radiused at the joint such that the desired shapeof the gap has radiused sides. Accordingly, determining the size andshape of the thermoset material joint gap at 410 can include determiningthe desired radius of curvature of the sides of the joint gap aftercuring.

After the size and shape of the joint gap is determined at 410, themethod 400 includes pre-forming a thermoplastic filler based on the sizeand shape of the thermoset material joint gap at 420. Pre-forming thethermoplastic filler means forming or making the thermoplastic fillerbefore the joint is formed. In some implementations, the thermoplasticfiller is pre-formed at 420 to have substantially the same size andshape as the size and shape of the joint gap determined at 410.Therefore, the thermoplastic filler can be pre-formed at 420 to have oneor more concave surfaces corresponding to bent portions of the thermosetmaterial. Pre-forming the thermoplastic filler at 420 can includemelting and/or pressurizing a thermoplastic material into a pliablestate, and molding the pliable thermoplastic material into a desirablesize and shape using a mold or die. The molded thermoplastic material isthen allowed to cool, which hardens the material into the desirable sizeand shape. In other implementations, pre-forming the thermoplasticfiller at 420 includes machining a hard piece or billet of thermoplasticmaterial into the desirable size and shape. Further, pre-forming thethermoplastic filler at 420 may include forming (e.g., cutting) athermoplastic material having a desired cross-sectional shape into adesired length.

After the thermoplastic filler is formed at 420, the method 400 includespositioning uncured thermoset material about the pre-formedthermoplastic filler at 430. In certain implementations, step 430 of themethod 400 includes positioning or arranging the uncured thermosetmaterial into the desired configuration adjoining each other about thepre-formed thermoplastic filler to form the joint. Step 430 can includepositioning two, three, or more layers of uncured thermoset materialabout the pre-formed thermoplastic filler. In some implementations,positioning the uncured thermoset material about the pre-formedthermoplastic filler can include applying the uncured thermoset materialonto the pre-formed thermoplastic filler such that the filler supportsthe uncured thermoset material in place. The thermoset material can be acomposite material (e.g., fibrous material) with a thermoset matrix.Further, the uncured thermoset material can be a pre-impregnated anduncured sheet of composite material.

With the uncured thermoset material positioned about the pre-formedthermoplastic filler, the method 400 includes thermally curing thethermoset material at 440, which concurrently bonds together thethermoset material and thermoplastic filler to form a joint. Due to thechemical properties of the thermoset material, curing the thermosetmaterial at 440 permanently sets or hardens the thermoset material aboutthe pre-formed thermoplastic filler. Thermally curing the thermosetmaterial at 440 includes applying heat at or above a desired curingtemperature to the thermoset material. The desired curing temperature isbelow the melting temperature of the thermoplastic material forming thefiller. Therefore, thermally curing the thermoset material at 440 doesnot melt or destabilize the pre-formed thermoplastic filler.

In the above description, certain terms may be used such as “up,”“down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,”“over,” “under” and the like. These terms are used, where applicable, toprovide some clarity of description when dealing with relativerelationships. But, these terms are not intended to imply absoluterelationships, positions, and/or orientations. For example, with respectto an object, an “upper” surface can become a “lower” surface simply byturning the object over. Nevertheless, it is still the same object.Further, the terms “including,” “comprising,” “having,” and variationsthereof mean “including but not limited to” unless expressly specifiedotherwise. An enumerated listing of items does not imply that any or allof the items are mutually exclusive and/or mutually inclusive, unlessexpressly specified otherwise. The terms “a,” “an,” and “the” also referto “one or more” unless expressly specified otherwise. Further, the term“plurality” can be defined as “at least two.”

Additionally, instances in this specification where one element is“coupled” to another element can include direct and indirect coupling.Direct coupling can be defined as one element coupled to and in somecontact with another element. Indirect coupling can be defined ascoupling between two elements not in direct contact with each other, buthaving one or more additional elements between the coupled elements.Further, as used herein, securing one element to another element caninclude direct securing and indirect securing. Additionally, as usedherein, “adjacent” does not necessarily denote contact. For example, oneelement can be adjacent another element without being in contact withthat element.

As used herein, the phrase “at least one of”, when used with a list ofitems, means different combinations of one or more of the listed itemsmay be used and only one of the items in the list may be needed. Theitem may be a particular object, thing, or category. In other words, “atleast one of” means any combination of items or number of items may beused from the list, but not all of the items in the list may berequired. For example, “at least one of item A, item B, and item C” maymean item A; item A and item B; item B; item A, item B, and item C; oritem B and item C. In some cases, “at least one of item A, item B, anditem C” may mean, for example, without limitation, two of item A, one ofitem B, and ten of item C; four of item B and seven of item C; or someother suitable combination.

The present subject matter may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is: 1-20. (canceled)
 21. A method for making a joint fora structure, comprising: forming a thermoplastic filler made from athermoplastic material; applying an uncured first thermoset layer ontothe thermoplastic filler, the uncured first thermoset layer comprising afirst fibrous material embedded in a first thermoset matrix; applying anuncured second thermoset layer onto the thermoplastic filler and intocontact with the uncured first thermoset layer, the uncured secondthermoset layer comprising a second fibrous material embedded in asecond thermoset matrix; and while the uncured first and secondthermoset layers are applied onto the thermoplastic filler and while theuncured second thermoset layer contacts the uncured first thermosetlayer, curing the uncured first thermoset layer and the second thermosetlayer to for a cured first thermoset layer and a cured second thermosetlayer and bond together the cured first thermoset layer, the curedsecond thermoset layer, and the thermoplastic filler.
 22. The method ofclaim 21, wherein the uncured first and second thermoset layers arecured at a temperature below a melting temperature of the thermoplasticmaterial.
 23. The method of claim 21, further comprising applying anuncured third thermoset layer onto the thermoplastic filler, the uncuredthird thermoset layer comprising a third fibrous material embedded in athird thermoset matrix.
 24. The method of claim 21, wherein forming thethermoplastic filler comprises compression molding the thermoplasticmaterial.
 25. The method of claim 21, wherein forming the thermoplasticfiller comprises extruding the thermoplastic material.
 26. The method ofclaim 21, wherein forming the thermoplastic filler comprises forming atleast one concave surface in the thermoplastic filler, and whereinapplying the uncured first thermoset layer onto the thermoplastic fillercomprises bending the uncured first thermoset layer along the at leastone concave surface, and curing the uncured first thermoset layercomprises curing the uncured first thermoset layer while bent along theat least one concave surface.
 27. A method for making a joint for astructure, comprising: forming a thermoplastic filler made from athermoplastic material; applying an uncured first thermoset layer ontothe thermoplastic filler, the uncured first thermoset layer comprising afirst fibrous material embedded in a first thermoset matrix; applying anuncured second thermoset layer onto the thermoplastic filler and intocontact with the uncured first thermoset layer, the uncured secondthermoset layer comprising a second fibrous material embedded in asecond thermoset matrix; and while the uncured first thermoset layer andthe uncured second thermoset layers are applied onto the thermoplasticfiller and while the uncured second thermoset layer contacts the uncuredfirst thermoset layer, curing the uncured first thermoset layer and theuncured second thermoset layer to form a cured first thermoset layer anda cured second thermoset layer and bond together the cured firstthermoset layer, the cured second thermoset layer, and the thermoplasticfiller without melting the thermoplastic filler.
 28. The method of claim27, further comprising applying an uncured third thermoset layer ontothe thermoplastic filler and wherein the uncured third thermoset layercomprises a third fibrous material, embedded in a third thermosetmatrix.
 29. The method of claim 27, wherein forming the thermoplasticfiller comprises compression molding the thermoplastic material.
 30. Themethod of claim 27, wherein forming the thermoplastic filler comprisesextruding the thermoplastic material.
 31. The method of claim 27,wherein forming the thermoplastic filler comprises forming thethermoplastic filler with an asymmetrical geometry.
 32. The method ofclaim 27, wherein forming the thermoplastic filler comprises forming aflat surface on the thermoplastic filler.
 33. The method of claim 27,wherein forming the thermoplastic filler comprises embeddingreinforcement fibers into the thermoplastic material.
 34. The method ofclaim 27, wherein forming the thermoplastic filler comprises forming thethermoplastic filler to be approximately equal in length to at least oneof: the uncured first thermoset layer along a region of the uncuredfirst thermoset layer to be bonded to the thermoplastic filler or theuncured second thermoset layer along a region of the uncured secondthermoset layer to be bonded to the thermoplastic filler.
 35. The methodof claim 27, wherein forming the thermoplastic filler comprises formingthe thermoplastic filler to be different in length from at least one of:the uncured first thermoset layer along a region of the uncured firstthermoset layer to be bonded to the thermoplastic filler or the uncuredsecond thermoset layer along a region of the uncured second thermosetlayer to be bonded to the thermoplastic filler.
 36. The method of claim27, wherein forming the thermoplastic filler comprises forming at leastone concave surface in the thermoplastic filler, and wherein applyingthe uncured first thermoset layer onto the thermoplastic fillercomprises bending the uncured first thermoset layer along the at leastone concave surface and curing the uncured first thermoset layercomprises curing the uncured first thermoset layer while bent along theat least one concave surface.
 37. The method of claim 27, wherein amelting temperature of the thermoplastic material of the thermoplasticfiller is between about 450° F. and about 650° F.
 38. A method forforming a joint, the method comprising: forming a first thermoset layercomprising a first fibrous material, embedded in a first thermosetmatrix, and a first portion, having a first shape; forming a secondthermoset layer comprising a second fibrous material, embedded in asecond thermoset matrix, and a second portion, having a second shape,the second thermoset layer being coupled to the first thermoset layer toform the joint, wherein a gap is defined between the first thermosetlayer and the second thermoset layer; forming a thermoplastic fillercomprising a thermoplastic material and unidirectional reinforcementfibers, the thermoplastic filler; positioning the thermoplastic fillerwithin the gap, and wherein: the thermoplastic material of thethermoplastic filler has a melting temperature that is greater than acure temperature of each of the first thermoset matrix and the secondthermoset matrix, the melting temperature of the thermoplastic materialof the thermoplastic filler is between about 450° F. and about 750° F.,and the thermoplastic filler supports and maintains the first shape ofthe first portion of the first thermoset layer and the second shape ofthe second portion of the second thermoset layer; and curing the firstthermoset layer and the second thermoset layer without melting thethermoplastic material of the thermoplastic filler.
 39. The method ofclaim 38, further comprising applying a third thermoset layer onto thethermoplastic filler, the third thermoset layer comprising a thirdfibrous material embedded in a third thermoset matrix.
 40. The method ofclaim 38, wherein forming the thermoplastic filler comprises forming atleast one concave surface in the thermoplastic filler, and the firstthermoset layer being applied onto the thermoplastic filler by bendingthe first thermoset layer along the at least one concave surface andcuring the first thermoset layer comprises curing the first thermosetlayer while bent along the at least one concave surface.